Re: [PATCH] virtio-balloon: correct used length

[Michael S. Tsirkin]

On Wed, Nov 24, 2021 at 12:32:55PM +0800, Jason Wang wrote:
> Spec said:
> 
> "and len the total of bytes written into the buffer."
> 
> For inflateq, deflateq and statsq, we don't process in_sg so the used
> length should be zero. For free_page_vq, though the free pages are
> supplied via in_sgs, zero used length should still be fine since
> anyway driver is expected to use the length in this case and it
> simplifies the error handling path.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>

I think for free page vq the point is that the pages are
zeroed by hypervisor, so we must set used len accordingly. No?

> ---
>  hw/virtio/virtio-balloon.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index c6962fcbfe..3e52daa793 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -231,7 +231,7 @@ static void balloon_stats_poll_cb(void *opaque)
>          return;
>      }
>  
> -    virtqueue_push(s->svq, s->stats_vq_elem, s->stats_vq_offset);
> +    virtqueue_push(s->svq, s->stats_vq_elem, 0);
>      virtio_notify(vdev, s->svq);
>      g_free(s->stats_vq_elem);
>      s->stats_vq_elem = NULL;
> @@ -438,7 +438,7 @@ static void virtio_balloon_handle_output(VirtIODevice 
> *vdev, VirtQueue *vq)
>              memory_region_unref(section.mr);
>          }
>  
> -        virtqueue_push(vq, elem, offset);
> +        virtqueue_push(vq, elem, 0);
>          virtio_notify(vdev, vq);
>          g_free(elem);
>          virtio_balloon_pbp_free(&pbp);
> @@ -549,7 +549,7 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
>      }
>  
>  out:
> -    virtqueue_push(vq, elem, 1);
> +    virtqueue_push(vq, elem, 0);
>      g_free(elem);
>      return ret;
>  }
> -- 
> 2.25.1